1. Field of the Invention
The present invention relates to an apparatus and method for coding and decoding CQI (Channel Quality Indicator) information in a communication system using an HSDPA (High Speed Downlink Packet Access), and more particularly to an apparatus and method for coding and decoding CQI information to insert a pilot signal into an HS-PDSCH (High Speed-Physical Downlink Shared CHannel) and transmit the HS-PDSCH having the pilot signal inserted therein such that power of a high speed uplink control channel can be controlled.
2. Description of the Related Art
Standardization of an HSDPA (High Speed Downlink Packet Access) based on high-speed downlink data transmission technologies is actively conducted in the 3GPP (Third Generation Partnership Project). First, a UMTS (Universal Mobile Telecommunications system) will be described.
FIG. 1 is an overview illustrating a structure of the UMTS. The UTMS includes a core network 100, a plurality of RNSs (Radio Network Subsystems) 110 and 120, and UE (User Equipment) 130, wherein the UE 130 can also be referred to as a user. The RNSs 110 and 120 are configured by RNCs (Radio Network Controllers) 111 and 112 and a plurality of Node-Bs 113, 114, 115 and 116, wherein a Node-B can also be referred to as a cell. An RNC is referred to as an SRNC (Serving RNC), a DRNC (Drift RNC) or a CRNC (Controlling RNC) according to the RNC's function. Alternatively, the SRNC and the DRNC can be classified by the UE's role.
Hereinafter, the RNCs will be described in detail. The SRNC is an RNC for managing UE information and communicating data with the core network 100. When UE data is transmitted and received through an RNC other than the SRNC, the above-described RNC is the DRNC. The CRNC is an RNC in the process of controlling Node-Bs.
The above-described RNCs will be described with reference to FIG. 1. When the RNC 111 manages information of the UE 130, the RNC 111 becomes the SRNC. When the UE 130 moves and data of the UE 130 is transmitted and received through the RNC 112, the RNC 112 becomes the DRNC. The RNC 111 controlling a Node-B 113 becomes the CRNC corresponding to the Node-B 113.
As described above, the standardization of the HSDPA based on the high-speed downlink data transmission technologies is actively conducted in the 3GPP. Moreover, many fields relating to the HSDPA are discussed. The HSDPA will be described on the basis of contents discussed up to now. The high-speed downlink data transmission is implemented by using a plurality of OVSF codes, adaptive channel coding, and HARQ (Hybrid Automatic Retransmission Request) based on a fast retransmission and soft combining. The maximum number of OVSF (Orthogonal Variable Spreading Factor) codes applicable to one user is 15, and a modulation scheme based on QPSK (Quadrature Phase Shift Keying), 16QAM (Quadrature Amplitude Modulation) or 64QAM is adaptively selected according to channel states. When erroneous data is detected, the data is retransmitted between UE and a Node-B and then the soft combining for a plurality of data is carried out, thereby improving overall communication efficiency. At this time, the retransmission is based on an n-channel SAW HARQ (Stop And Wait Hybrid Automatic Retransmission Request) process.
The n-channel SAW HARQ process will be described in detail. Two new approaches are introduced to the n-channel SAW HARQ process for the HSDPA in order to improve a conventional SAW ARQ (Stop And Wait Automatic Retransmission Request) process.
First, a receiving side temporarily stores erroneous data and combines the erroneous data and retransmitted data, thereby reducing a probability of error occurrence. This is called soft combining. The soft combining is classified into CC (Chase Combining) and IR (Incremental Redundancy). In relation to the CC, a transmitting side uses the same format for a first transmission and retransmission. If m symbols have been transmitted as one coded block at the time of the first transmission, the same m symbols are also retransmitted at the time of the retransmission. That is, the same coding rate is applied to the first transmission and retransmissions. Accordingly, the receiving side combines a first transmitted coded block with a retransmitted coded block, performs a CRC (Cyclic Redundancy Code) check using the combined coded blocks and determines whether an error has been generated.
Next, the IR will be described. In relation to the IR, the transmitting side uses different formats for the first transmission and retransmissions. If n-bit user data has been coded to the m symbols, the transmitting side transmits only a portion of the m symbols at the time of the first transmission and sequentially retransmits remaining portions at the time of the retransmission. For this reason, transmission bits at the first transmission and retransmission are different. Accordingly, the receiving side adds bits received at the first transmission to non-redundant bits received at the retransmission and executes error correction after configuring a coding block having a higher coding rate. In relation to the IR, the first transmission and respective retransmissions are classified by RV (Redundancy Version) values. Thus, the first transmission is referred to as RV 1 a retransmission subsequent to the first transmission is referred to as RV 2 and another retransmission subsequent to the retransmission is referred to as RV 3. The receiving side combines a first transmitted coded block with a retransmitted coded block using version information. An RV value contained in Part-2 of an HS-SCCH (High Speed-Shared Control CHannel) indicates the above-described version information.
The second approach introduced to improve the efficiency of the conventional SAW ARQ process, is as follows. The conventional SAW ARQ process can transmit a next packet only when an ACK (positive acknowledgement) for a previous packet is received, but the n-channel SAW HARQ process can consecutively transmit a plurality of packets in the case where the ACK is not received, thereby improving the utility of a radio link. If n logical channels between UE and a Node-B are configured and the channels are identified by channel numbers in the n-channel SAW HARQ process, the UE on the receiving side can identify a certain channel to which a received packet belongs at an arbitrary point of time. Moreover, the UE can re-configure received packets in order and take necessary actions such as soft combining of a corresponding packet, etc.
The n-channel SAW HARQ process will be described in detail with reference to FIG. 1. It is assumed that a 4-channel SAW HARQ process is carried out between an arbitrary Node-B 113 and UE 130, and logical identifiers of 1 to 4 are allocated to respective channels. A physical layer between the UE 130 and the Node-B 113 has an HARQ processor corresponding to each channel. The Node-B 113 allocates a channel identifier “1” to a first transmitted coded block (indicating user data transmitted in one TTI (Transmission Time Interval)) and transmits it to the UE 130. If an error has been generated in a corresponding coded block, the UE 130 transfers a coded block to a first HARQ processor 1 corresponding to a channel 1 using the channel identifier, and transmits an NACK (negative acknowledgement) to the channel 1. On the other hand, the Node-B 113 transmits a subsequently coded block to a channel 2 irrespective of the reception of the ACK for the coded block of the channel 1. If an error has been generated also at the subsequently coded block, the coded block is transferred to a corresponding HARQ processor. When the Node-B 113 receives the NACK for the coded block of the channel 1 from the UE 130, it retransmits a corresponding coded block to the channel 1. Thus, the UE 130 transfers the coded block to the first HARQ processor 1 using a channel identifier of the coded block. The first HARQ processor 1 of the UE 130 carries out soft combining for a previously stored coded block and a retransmitted coded block. As described above, the n-channel SAW HARQ process corresponds a channel identifier to an HARQ processor with a one-to-one correspondence. Without delaying user data transmission until the ACK is received, the n-channel SAW HARQ process can appropriately correspond a first transmitted coded block to a retransmitted coded block.
A plurality of UEs can simultaneously use a number of OVSF codes available in the HSDPA. Namely, there is possible concurrent OVSF code multiplexing between the UEs. The concurrent OVSF code multiplexing will be described with reference to FIG. 2.
FIG. 2 shows an exemplary OVSF code assignment in a conventional HSDPA system. The case where an SF (Spreading Factor) is 16 as shown in FIG. 2, will be described.
Referring to FIG. 2, respective OVSF codes can be represented as C(i, j) on the basis of the OVSF code tree. A parameter i of C(i, j) is a value of an SF, and a parameter j of C(i, j) is a code number. For example, when an OVSF code is C(16, 0), an SF is 16 and a code number is 0. At this time, C(16, 0) is a first code of SF=16 in the OVSF code tree. FIG. 2 shows the case where 15 OVSF codes, i.e., C(16, 0) to C(16, 14) corresponding to 1st code to 15th code of SF=16, are assigned in an HSDPA communication system. The 15 OVSF codes for the UEs can be multiplexed. For example, OVSF codes as shown in the following Table 1 can be multiplexed.
TABLE 1ABCT0C(16, 0)~C(16, 5)C(16, 6)~C(16, 10)C(16, 11)~C(16, 14)T1C(16, 0)~C(16, 3)C(16, 4)~C(16, 14)—T2C(16, 0)~C(16, 3)C(16, 4)~C(16, 5)C(16, 6)~C(16, 14)
In the above Table 1, A, B and C are arbitrary users, i.e., arbitrary UEs using the HSDPA communication system. As shown in the above Table 1, the UEs A, B and C multiplex OVSF codes assigned to the HSDPA communication system at periods of time T0, T1 and T2. The number of OVSF codes assigned to the UEs and OVSF code positions in the OVSF code tree are determined by the Node-B, utilizing parameters such as the amount of user data of the UE stored in the Node-B, a channel state between the Node-B and UE, etc.
Control information exchanged between the Node-B and UE includes the number of OVSF codes available in the arbitrary UE, code information associated with positions designated on the OVSF code tree, channel quality information needed for determining an adaptive modulation scheme according to a channel state, modulation information, channel number information needed for supporting the n-channel SAW HARQ process, ACK/NACK information, etc. Hereinafter, channels used for transmitting the control information and user data will be described.
The types of channels used in the HSDPA other than channels used in a conventional WCDMA (Wideband Code Division Multiple Access) system are classified by a downlink and uplink as follows. First, downlink channels include an HS-SCCH (High Speed-Shared Control CHannel), an associated DPCH (Dedicated Physical CHannel), and an HS-PDSCH (High Speed-Physical Downlink Shared CHannel), while an uplink channel includes an HS-DPCCH (High Speed-Dedicated Physical Control CHannel).
Timing relations of the channels are shown in FIG. 3. First, the UE measures channel quality between the UE and a Node-B using PCPICH (Primary Common Pilot CHannel), etc., and notifies the Node-B of a result of the measurement through a CQI (Channel Quality Indicator). The CQI is transmitted through the HS-DPCCH. The Node-B carries out a scheduling function using the CQI. The scheduling function decides which UE is to actually receive data for a next TTI among UEs receiving an HSDPA service within the same cell. The scheduling function also decides a modulation scheme to be used for a data transmission, the number of codes to be assigned, etc. If the data transmission for an arbitrary UE is decided, the Node-B transmits control information 301 needed for receiving the data through at least one HS-SCCH. At this time, the UE can identify the HS-SCCH to be received using a UE ID. Moreover, the UE needs to receive a maximum of four HS-SCCHs with considering UE complexity. One cell can easily schedule packet data by operating more than the four HS-SCCHs. A set of HS-SCCHs assigned to the arbitrary UE is referred to as a serving HS-SCCH set. The serving HS-SCCH set can be designated on a UE-by-UE basis. Other details will be described below.
The control information 301 contained in the HS-SCCH is as follows. The control information 301 includes 7-bit information associated with OVSF codes to be used in the HS-PDSCH (hereinafter, referred to as “code information 302”), 1-bit information indicating a modulation scheme to be applied to the HS-PDSCH, 6-bit information indicating a size of data to be sent through the HS-PDSCH, and HARQ information. The HARQ information consists of 7 bits including 1-bit information of a new data indicator indicating whether data to be sent through the HS-PDSCH is new data or not, 3-bit information relating to an RV value of data to be sent through the HS-PDSCH, and a 3-bit channel number associated with n-channel SAW HARQ of data to be sent through the HS-PDSCH. FIG. 4 shows a structure of the HS-SCCH.
As shown in FIG. 4, the HS-SCCH is transmitted on the basis of OVSF codes of SF=128, and divided into three parts of Part-1, Part-2 and a CRC. The 8 Part-1 information bits is coded with 40 bits in a first slot of an HS-SCCH frame, and the 13 Part-2 information bits and 16 CRC information bits are coded with 80 bits in second and third slots of the HS-SCCH frame. UE carries out individual channel codings of the Part-1 information and the Part-2 information. Although the UE receives only the Part-1 information in the first slot, the UE can identify which of the four HS-SCCHs sends control information needed for receiving an HS-PDSCH.
The Part-1 information includes code information indicating positions on the code tree of OVSF codes to be used in certain UE, the number of the OVSF codes, and modulation scheme information. FIG. 5 shows a scrambler based on the channel coding of the Part-1 information and UE ID needed for identifying UE after receiving the Part-1 information. The Part-1 information is coded by a rate ½ convolutional coder and then rate-matched producing 40 bits corresponding to one slot through a rate-matching algorithm. A 10-bit UE ID is coded by a (32, 10) block code used in coding of TFCI (Transport-Format-Combination Indicator) based on Rel. '99 specifications and then 32 bits are produced. The produced 32 bits are then extended to 40 bits by repeating the first 8 bits. The 40 bits based on the Part-1 information are XORed with 40 bits based on the UE ID. As a result, a scrambling procedure based on the UE ID is completed.
The Part-2 information includes information relating to a size of a TB (Transport Block) indicating a length of data to be sent through the HS-PDSCH, a channel number of n-channel SAW HARQ, a new data indicator indicating whether corresponding data is new data or retransmission data, and an RV value indicating which version the corresponding data is based on, in relation to the IR.
The CRC information includes a result of a CRC check for the Part-1 information and the UE ID. The UE ID may consist of 10 bits and the UE ID itself is not separately sent. The transmitting and receiving sides produce the UE ID at a time of calculating a CRC, respectively. Thus, the UE can identify whether information contained in an arbitrary HS-SCCH is its own information or not. For example, where control information is transmitted to UE A through the HS-SCCH, a Node-B produces the CRC using the Part-1 and Part-2 information and the UE A's ID. When the UE A calculates a CRC using its own UE ID and the Part-1 and Part-2 information, it determines that the control information has been successfully received through the HS-SCCH if an error is not detected by the CRC check.
An operation of the UE receiving HS-SCCHs is as follows. The UE generates a scrambling sequence using a stored UE ID, scrambles an HS-SCCH corresponding to a first slot in four HS-SCCHs, and performs Viterbi decoding of a convolutional code. Then, the UE identifies the HS-SCCHs allocated to its own UE and receives control information needed for receiving the HS-SCCHs. After receiving the control information of the HS-SCCHs, the UE calculates a CRC using the Part-1 and Part-2 information and its own UE ID, and determines that the control information has been successfully received if an error is not detected in the CRC check. Then, decoding of HS-PDSCH information is performed and the decoding is stopped if an error is detected in the CRC check.
The UE performs necessary operations such as demodulation of data received through the HS-PDSCH on the basis of the information received through the HS-SCCH. At this time, through code information, the UE determines whether it receives an HS-PDSCH based on what OVSF code and determines how to demodulate the HS-PDSCH on the basis of modulation information. The UE decodes data received through the HS-PDSCH. After the decoding procedure is completed, the UE determines whether erroneous data is detected in a CRC check and then transmits ACK/NACK information. That is, if erroneous data is not detected, the ACK in transmitted. Otherwise, the NACK is transmitted.
The UE transmits the ACK/NACK information for packet data and CQI information associated with a downlink channel state through an HS-DPCCH. A structure of the HS-DPCCH is shown in FIG. 6. In terms of the HS-DPCCH, a spreading factor SF=256 and an HS-DPCCH sub-frame corresponds to three slots. The ACK/NACK information is transmitted in a first slot of the HS-DPCCH sub-frame. In second and third slots of the HS-DPCCH sub-frame, the CQI information is transmitted. One-bit ACK/NACK information is repeated ten times such that 10 bits can be outputted. Five-bit CQI information is coded by (20, 5) channel coding such that 20 bits can be outputted.
That is, the CQI information is provided to identify a state of a downlink channel. The CQI information is needed to identify the channel's state. Hence, when UE or a system is implemented, its complexity increases in channel coding and decoding.